Rounding out Part 1, Kathleen Bawn, Knox Brown, Angela X. Ocampo, Shawn Patterson, Jr., John L. Ray, and John Zaller report results from one of the largest “on the ground” studies of candidate selection ever undertaken. Focusing on fifty-three potentially winnable open seat House races in the 2013–14 election cycle, the authors interviewed local participants and observers to probe the processes behind candidate selection in primary elections. The extensive fieldwork reveals that groups, which may include local party organizations, are the central political actors in the selection process. Voters rely on signals from the groups, whose primary objective is to minimize uncertainty about a candidate’s commitment to particular policy goals. Because this objective may lead groups to promote nominees who are not closest to the primary electorates’ ideological preferences, the candidates who win may be more ideologically extreme than even the primary electorates are. The chapter therefore highlights how analyses that focus on the general election, such as Chapters 2 and 6, are dependent on the candidates that emerge from the primary selection process.